In recent years, in particular, materials for forming a color image have been mainly used as an image recording material. Specifically, recording materials of inkjet system, recording materials of heat-sensitive transfer system, recording materials of electrophotographic system, silver halide photosensitive materials of transfer system, printing inks, recording pens, and the like, have been used extensively. Color filters are used in image pick-up elements, such as CCD for photographing equipment, and in displays, such as LCD and PDP, to record and reproduce color images.
In these color image recording materials and color filters, colorants (dyes or pigments) of three primary colors based on a so-called additive color mixing method or subtractive color mixing method are used, to reproduce (display) or record full-color images. A colorant, which has absorption characteristics that enable the acquisition of a preferred color reproduction range and has (color) fastness against various conditions for use is not available yet, and improvement is strongly desired.
As the heat-sensitive transfer recording method, there are a process including the steps of heating a heat-sensitive transfer material having a base film (support) and a hot-melt ink layer formed thereon with a thermal head, and recording the melted ink to an image-receiving material; and a process including the steps of heating a heat-sensitive transfer material having a base film and a dye-providing layer formed thereon that contains a heat transfer dye with a thermal head, and thermal diffusion transferring the dye to an image-receiving material. The latter heat-sensitive transfer process enables to change a transfer amount of the dye by altering energy applied to a thermal head, so that a gradation recording is easily achieved. Consequently, such the process is especially advantageous to a high quality full color recording. However, because the heat transfer dye used in the process is limited from various aspects, only a considerably few dye satisfies all the performances required for the process.
As the performances required for the process, there are, for example, spectral characteristics preferred in terms of color reproduction, easiness of transfer, light resistance and heat resistance, fastness to various chemicals, easiness of synthesis, and easiness of production of heat-sensitive transfer recording materials.
As the dye having both spectral characteristics preferred in terms of color reproduction and fastness to light and heat, the dyes disclosed in JP-A-1-225592 (“JP-A” means unexamined published Japanese patent application) and JP-A-63-189289 can be mentioned as examples. The transfer sensitivities of these dyes were sufficient for the heat-sensitive transfer recording at the time when such the inventions were disclosed in these publications, but were not sufficient for the current high-speed-transfer type heat-sensitive transfer recording. Accordingly, there is a demand for improvement in transfer sensitivity.
As the dyes that are excellent in transfer sensitivity, the dyes disclosed in JP-A-3-108583, JP-A-63-182193, JP-B-4-47635 (“JP-B” means examined Japanese patent publication) and JP-B-4-22714 can be mentioned as examples. However, as a result of promotion (speeding up) in a transfer speed according to a recent progress in technology, many dyes are not enough to fulfill the requirements for transfer sensitivity. Among these dyes, as the dyes that show excellent transfer sensitivity even in the high-speed-transfer type heat-sensitive transfer recording, the dyes disclosed in publication of JP-A-3-108583 can be mentioned as examples. However, these dyes are not satisfactory in terms of fastness to light and heat. Therefore, compatibility of high speed transferring property and fastness has been strongly desired.
On the other hand, a dye having a high solubility to a solvent enables not only reduction of a working load for dissolving a dye at the time when a heat-sensitive transfer ink sheet is prepared, but also preparation of a highly concentrated ink sheet solution. Consequently, such the dye is useful because a use amount of organic solvents can be saved, which results in reduction of load to environment. Therefore, it has been desired to develop a heat-sensitive transfer dye having a high solubility to a solvent.
Generally, toners containing a colorant dispersed in resin particles are widely used in color copiers and color laser printers of electrophotographic system. The properties required for the color toners include absorption characteristics that enable the acquisition of a preferred color reproduction range, high transmission (transparency) which becomes a problem in particular, when they are used in an over head projector (OHP); and (color) fastness against various factors under environmental conditions when using. Toners containing a pigment as a colorant dispersed in particles are disclosed in JP-A-62-157051, JP-A-62-255956 and JP-A-6-118715. Although these toners have excellent light resistance, they easily aggregate since they are insoluble in a solvent, thereby causing problems such as a reduction in transparency and a change in hue of transmitted color. On the other hand, toners containing a dye as a colorant are disclosed in JP-A-3-276161, JP-A-2-207274 and JP-A-2-207273. These toners have rather high transparency and have no change in hue but have a problem with light resistance.
Because of inexpensive material costs, capability of high-speed recording, reduced noise in recording operations, and ease in color recording, inkjet recording has rapidly come into wide use and is being further developed.
Inkjet recording methods include a continuous method in which droplets are supplied continuously and an on-demand method in which droplets are supplied in response to an image information signal. Ink discharge systems include: 1) one in which droplets are discharged by applying pressure with a piezoelectric element, 2) one in which droplets are discharged by producing air bubbles in ink with heat, 3) one using ultrasonic waves, and 4) one in which droplets are discharged by electrostatic suction. Aqueous ink, oil-based ink, and solid (fusible) ink are used as inkjet-recording ink.
The properties required for a colorant that is used in the inkjet-recording ink are: good solubility or dispersibility in a solvent; capability of high-density recording; good hue; fastness to light, heat, an active gas in environment (e.g. oxidative gases such as ozone, NOx, as well as SOx); excellent fastness to water and chemicals; good fixation and little blur on image-receiving materials; excellent storability as ink; being free from toxicity; high purity; and being available inexpensively. However, it is very difficult to provide a colorant that satisfies these requirements on a high level. Particularly, it is desired that a colorant should have a good yellow hue, high solubility, and fastness to light, humidity and heat, and in particular, fastness to light is strongly desired.
Since a color filter needs to have high transparency, a method called a dyeing method, in which the color filter is colored with a dye, has been carried out. For instance, a photoresist which can be dyed is subjected to pattern exposure and development to form a pattern, and then the resulting pattern is dyed with a dye of filter color. Subsequently, these steps are repeated for all the colors of the filter, to produce a color filter. Besides the above dyeing method, a color filter can also be produced by a method using a positive-type resist. These methods provide a color filter which has high transmittance due to use of a dye, thereby being excellent in optical characteristics, but which has limitations, for example, to light resistance and heat resistance. Therefore, a dye which has excellent resistance to various factors and high transparency has been desired. Meanwhile, a method of using an organic pigment having excellent light resistance and heat resistance in place of a dye is widely known, but a color filter employing a pigment hardly gives optical properties equivalent to those employing a dye.
Dyes for use in the above various applications must have the following properties in common. That is, they must have, for example, a hue preferred from the viewpoint of color reproduction, an optimum spectral absorption, excellent fastness-properties such as light resistance, humidity resistance and chemical resistance, and a high solubility.
On the other hand, azo dyes having an azo bond at the 3-position of a pyrazole ring are disclosed in publications of JP-A-2005-162812 and JP-A-2003-41160, JP-A-2003-41161, JP-A-2003-41162, JP-A-2003-41163, JP-A-2003-128953, JP-A-2002-194258, and JP-A-8-231867, and azo dyes having a particular structure formed from a pyrazolotriazole coupling component are disclosed in publications of JP-A-63-110452 and JP-A-5-124364, JP-A-2001-147510, JP-A-2-24191, and UK Research Disclosure (1979), Vol. 181, page 247.